1. Field of the Invention
The present invention relates to a liquid jet recording head used for the execution of a liquid jet recording method or the like that performs print recording by discharging liquid from the discharge openings as droplets. The invention also relates to a method for manufacturing such head.
2. Related Background Art
In general, a liquid jet recording head which is usable for a liquid jet recording method comprises fine discharge openings (orifices) that discharge liquid (ink), discharge energy transducing devices (heat generating resistors, for example) arranged for a part of each of liquid flow paths, and a liquid supply opening for supplying liquid to the liquid flow paths. The liquid jet recording head is structured to perform print recording by applying driving signals to the discharge energy transducing devices (heat generating resistors) in accordance with image information inputted from the outside so that the discharge energy transducing devices (heat generating resistors) are allowed to generate the thermal energy, which gives an abrupt rise of temperature beyond the one that may cause nuclear boiling phenomenon of ink, and creates film boiling in it. Thus, the ink jet recording head forms bubbles in ink, and discharges ink from the discharge openings as droplets for print recording by means of the development and contraction of each of such bubbles.
As regards the structures and methods of manufacture for a liquid jet recording head of the kind, there have been known various types and methods. Using silicon wafer or other substrate a plurality of discharge energy transducing devices are arranged on the surface of such substrate to provide ink discharge energy. For each of discharge energy transducing devices, the corresponding nozzle unit (liquid flow paths) and a plurality of discharge openings are formed to discharge ink. Here, a conventionally known type is provided with an ink supply opening formed on the central part of the liquid jet recording head, which reaches the reverse side thereof in order to supply ink.
In accordance with FIGS. 6A to 6F, the description will be made of the processing steps of a liquid jet recording head of the kind. For a silicon wafer 101, SiO.sub.2 layers 102 are formed as the heat accumulation layer (FIG. 6A). On the surface thereof, there are laminated discharge energy transducing devices 103, electrodes (not shown), a protection layer (SiN) 104, and an anti-cavitation film. In this way, a pattern is formed (FIG. 6B). In this respect, the discharge energy transducing elements 103 are relatively arranged for the slit type ink supply opening which is formed afterward. Then, the positive type photoresist nozzle molding material is coated. After the pattern is formed, the nozzle member 106 (which is photosensitive epoxy resin, for example) is coated. Thus, the discharge openings 107 are formed by means of photolithography (FIG. 6C). After that, from the reverse side of the wafer 101, the SiO.sub.2 layer is removed by use of buffer hydrofluoric acid. Then, using resist pattern 108 a groove 109 is formed by means of anisotropic etching in order to provide the slit type ink supply opening. The anisotropic etching is suspended at the SiO.sub.2 layer 102 on the surface side (FIG. 6D). Subsequently, as shown in FIG. 6E, the SiO.sub.2 layer 102 is removed by use of buffer hydrofluoric acid. After that, deep ultraviolet light is irradiated onto the nozzle molding material 105 to make it soluble. Subsequently, the nozzle molding material 105 is removed. The electrode extrusions (hereinafter referred to as bumps) 111 are formed on the electrode pads, respectively. Then, the silicon wafer substrate is separated along the substrate separation line 110 which is shown in FIG. 6E, hence obtaining the substrate chip of the liquid jet recording head (FIG. 6F). Here, FIG. 6F shows a state where inner leads 115 of TAB tape, which are indicated by broken lines, are connected with bumps 111.
The liquid jet recording head produced by a method of manufacture of the kind makes it possible to form the discharge opening plate thinner for the nozzle unit. This, in turn, makes it possible to reduce the amount of discharged ink, thus obtaining the print recording in a high image quality. Also, using resin as material for the formation of discharge plate (a member to form ink flow paths) it becomes possible to apply a spin coating method to coating such material, and also, to form the discharge openings in the steps of exposure and development processes with the advantage that its processing and handling become easier.
Then, as a method for electrically assembling the chip of the liquid jet recording head whose nozzle unit and discharge openings have been formed in this way, there is the TAB assembling in which the inner leads of TAB tape are connected by means of inner lead bonding (ILB) with the bumps on the electrode pads arranged on the circumference of the chip, and then, after the inner leads and bumps are connected, each of the junctions is assembled. As compared with the wire bonding method, this TAB assembling enables a thinner assembling to suppress the height of the sealing resin and makes it lower. Also, the TAB assembling makes it easier to wipe off (or execute blading of) ink mist or the like which adheres to the surface of the discharge opening plate. Therefore, this method is easily applicable to the electrical assembling of the chip of the liquid jet recording head which is provided with the nozzle unit and discharge openings formed on it.
Then, for the ILB method for connecting the inner leads of the TAB tape with the bumps on the chip, there are, among some others, the single point bonding, and the gang bonding where a plurality of inner leads are connected with the bumps at a time. For the liquid jet recording head chip, the single point bonding method is adopted. The ILB bonder used for the single point bonding method comprises a chip stage that fixes and holds a chip like the one as shown in FIG. 6F, for example, and heats the bumps provided for the electrode pads on the chip at the same time, as well as a bonding tool to which ultrasonic waves are transmitted from the hone which is arranged above the chip stage. In this manner, the inner leads of the TAB tape are positioned with the bumps of the chip, which have been fixed and heated on the chip stage. Then, the structure is arranged so that the bonding tool is pressed to it. To the bonding tool, a load is given, while being oscillated by the application of ultrasonic waves. Hence, the TAB inner leads and the bumps are connected. Here, it is generally practiced to use a bonding tool having a cross-patterned extrusion at its tip as the one suitable for such structure, because this extrusion provides a better capability of gripping the inner leads while the ILB is being performed.
Since ultrasonic waves are used for the single point bonding of the inner leads of a TAB tape of the kind, the base film of the chip and the TAB tape should be fixed sufficiently by means of adsorption or the like. Otherwise, it is impossible to connect the bumps on the chip and the TAB inner leads appropriately. As a result, it becomes difficult to obtain its electrical connection reliably. In other words, when pulling tests are conducted after the completion of the ILB, there are often observed the modes that may indicate the lower reliability of the devices (such as a destructive mode where the bumps and inner leads are peeled off, a destructive mode where the chip silicon underneath the pads are cracked).
Here, a through hole is made on the chip of the liquid jet recording head in order to provide the ink supply opening that penetrates the central part of the chip. Therefore, it becomes impossible to obtain a sufficient area that may provide a surface large enough to fix the chip by means of appropriate adsorption. This situation hinders the provision of sufficient adsorption of the chip when the ILB is performed. Consequently, the chip may move while the ILB is being performed, often leading to the case where the modes may take place, such as peeling off the connection between the bumps and inner leads, cracking silicon underneath the pads. In this respect, if adsorption is intensified more in order to avoid the occurrence of such modes, the air in the chamber arranged for the ILB bonder is sucked through the discharge openings when the chip is adsorbed. As a result, the dust particles or the like contained in the air in such chamber may be allowed to adhere to the upper surface of discharge energy transducing devices (heat generating resistors), hence resulting in the unfavorable event that the ink discharge performance is significantly affected. In this respect, if the ILB is performed under the clean environment, such as in a clean booth or in a clean room, it may be possible to prevent the dust particles or the like from adhering to the upper surface of the discharge energy transducing devices (heat generating resistors). However, since this system inevitably needs the provision of a clean booth, a clean room, or some other facilities, as well as the control and operation thereof, a considerable amount of additional expenditures is required accordingly.
Also, it is conceivable that clamping may be adopted, instead of adsorption, for the chip fixation when the ILB is performed. However, chipping may be easily caused by clamping if the silicon substrate is used. As a result, it is not preferable to fix the silicon chip by means of clamping. Particularly, the discharge opening plate tends to be cracked or deformed when clamping the silicon chip used for the liquid jet recording head where the ink supply opening is provided for the central part thereof, because the discharge opening plate is formed by resin above such ink supply opening. Therefore, it is not preferable to perform the ILB while clamping the silicon chip to fix it.
Also, it is most common to use a bonding tool having a cross-patterned extrusion at its tip as the TAB tool for the execution of the single point bonding as described earlier. However, if the chip cannot be fixed by means of sufficient adsorption, there are observed many cases where silicon underneath the pads are broken in particular when the pulling tests are conducted for the inner leads after the completion of the ILB. It is then found that the production yield becomes unfavorable and far from satisfaction if the bonding tool, which is provided with the cross-patterned extrusion at its tip, is adopted for the ILB of the chip used for the liquid jet recording head.